Sorbus with curled leaves

OregonGrapeJuly 24, 2013

I have a Sorbus americana (American Mountain-ash) that is in its second summer growing in a full afternoon sun area in my backyard. It's in clay with a 2" layer of bark mulch on top and gets a heavy watering every other week. The leaves have been curled for the past month or so. As the photo shows, some of them have yellowing along the edge. Despite this, new growth has appeared over the past week.

Are the curled and slightly yellowing leaves a sign of a nutrition deficiency? Because I have manzanitas and penstemons growing in this area, I do not amend the soil. (If so, I may have to dig this tree up and grow it in a large container.) I've given this tree a little extra water over the past couple of weeks, but the leaves remain curled.

Yellow edges might indicate a minerals problem - either too much or not enough of something. Every other week might not be an adequately frequent watering interval for this eastern North American rainy climate tree. It certainly won't be culturally or visually compatible with dry climate manzanitas and penstemons - in addition to their physical requirements all plants have a related feature that has been called naturalistic character. If a plant is from a moist situation and looks the part it won't seem "right" in the same bed with dryland plants. It is true that in nature you see perhaps unexpected combinations, but the fact that these exist does not make them any more expected - in our gardens we create artificial arrangements of plants and other landscape elements that make us more comfortable than phenomenon encountered out in nature might.

Thanks, bboy. I'm acutely aware that the sorbus' plant community is far-removed from the drought-tolerant plants growing around it. (Though the nearby Wayside and Howard McMinn manzanitas and Penstemon Margarita BOP could probably tolerate once-a-week water.) I originally had Myrica californicas growing next to the sorbus, but have changed my landscaping significantly over the past year.

Your suggestion of a minerals problem makes sense, given that this sorbus did relatively well after I planted it last summer (while it still had the original fertilizer from the nursery in the root ball). The tree hasn't responded to the heavier watering that I've given it over the past couple of weeks.

Given that I can't fertilize in this area now, I will probably transplant the sorbus to a large container and give it a healthy dosage of slow-release fertilizer. Ceanothus sanguineus would probably do better in the ground in its spot.

The Myrica does grow quite large, unless closely sheared. The ceanothus is not very ornamental, but maybe you have it already. Those places in the Seattle area where I have seen it (once) and the much more striking Ceanothus velutinus (multiple times) are always hot slopes facing into the sun for at least part of the day - and where any taller trees are in the process of growing up around the site the ceanothus are declining.

Yeah, Ceanothus sanguineus isn't going to win any beauty contests. I'm going with this one mostly because of its thinner, more upright form. (I've got about a 3' diameter limit near the ground here... it can spread out more a few feet up.) This spot bakes in the afternoon/evening sun for 7+ hours at this time of the year.

For ornamental purposes, I have a 'Skylark' on the other side of the yard, right next to my deck. I'd love to grow more ceanothus, but I'm out of spots that are large enough, get full sun, and are summer-dry.

Shaded specimen with lower branches killed by competition. But you can get the same effect by pruning it. You can also get the same effect by pruning an upright-growing evergreen ceanothus, with it in addition being a much more attractive and interesting kind.